This invention relates to a catalyst component for use in the polymerization of .alpha.-olefins and to a process for the polymerization of .alpha.-olefins using the same, and more particularly, it pertains to a supported titanium catalyst component prepared by an improved process and with a process for producing a stereoregular homopolymer or copolymer of .alpha.-olefins using a catalyst system comprising the supported titanium catalyst component and an organo aluminum catalyst component.
For the stereoregular polymerization of .alpha.-olefins, it has hitherto been carried out to use a catalyst system comprising solid TiCl.sub.3, obtained by reducing TiCl.sub.4 by various methods, and an organo aluminum compound as cocatalyst. However, this method has many disadvantages on a commercial scale in that both the polymerization activity and stereoregularity of commercially available catalyst systems are low and steps for polymer deashing and for removing amorphous polymers are required. In order to overcome these disadvantages, there have been proposed processes for the polymerization of .alpha.-olefins by the use of catalyst systems comprising, by way of example, titanium catalyst components obtained by treating solids, obtained by reducing TiCl.sub.4 with organo aluminum compounds, with complexing agents and then with TiCl.sub.4 (Japanese Patent Publication No. 3356/1978) or by treating the solids with complexing agents and hexachloroethane (Japanese Patent Public Disclosure No. 107294/1977). In these examples, as far as solid TiCl.sub.3 is used, however, only a part of the titanium can be utilized as active catalyst and, consequently, there is not obtained such a high catalytic efficiency as to omit the polymer deashing step.
As a desirable method for raising the polymerization activity per unit titanium, on the other hand, it has been known to disperse and support titanium compounds on other solids. Actually, in the production of polyethylene by middle or low pressure process, a high catalytic efficiency can be achieved by the use of a catalyst system comprising a titanium catalyst component (titanium compounds on various supports) and an organo aluminum compound component. A polymeric product of good quality can be produced on a commercial scale without polymer deashing step. However, in the polymerization of higher .alpha.-olefins, e.g., propylene, a high polymerization activity as well as a high stereoregularity are required, resulting in a more difficult problem than in the case of producing polyethylene by middle or low pressure process.
Of late, various improved methods have been proposed as to the stereoregular polymerization of .alpha.-olefins using a catalyst system comprising a supported titanium catalyst component and an organo aluminum catalyst component. These methods are classified into two groups depending on the methods of supporting titanium, that is, (I) by cogrinding a support and titanium halide and (II) by suspending a support in a titanium halide and heating the slurry.
Examples of the type (I) are a method comprising using a catalyst system comprising a supported titanium catalyst component, obtained by cogrinding an anhydrous magnesium dihalide and tetravalent titanium halide or complex of a tetravalent titanium halide and, an electron donating compound, and an organo aluminum catalyst component consisting of an organo aluminum compound and electron donating compound (Japenese Patent Public Disclosure Nos. 16986-8/1973); a method comprising using a catalyst system composed of a supported titanium catalyst component obtained in a similar manner as set forth above except the cogrinding of materials is carried out in the presence of an organic solid such as durene, hexachlorobenzene or polyolefin and an inorganic solid such as lithium chloride, calcium chloride or alumina, which are substantially inert to the other compounds for composing the catalyst, and an organo aluminum catalyst component consisting of a trialkylaluminum and an electron donating compound (Japanese Patent Public Disclosure No. 86482/1974); and a method comprising using, in combination, a supported titanium catalyst component, obtained by cogrinding a magnesium alkoxide, titanium tetrahalide, electron donating compound and halosilane, and an organo aluminum catalyst component consisting of an organo aluminum compound and electron donating compound (Japanese Patent Public Disclosure No. 98076/1977).
These catalyst systems have an advantage in that titanium compounds can effectively be utilized and handling thereof is easy, but, on the other hand, a long time is required for grinding. In addition, as set forth in Japanese Patent Public Disclosure No. 16986/1973, the supported titanium catalyst obtained has a small surface area and gives unsatisfactory results in overall polymerization activity and stereoregularity sufficient for omitting the steps for polymer deashing and removing amorphous polymers in a polyolefin commercial operation.
Examples of the type (II) are a method comprising ball milling an anhydrous magnesium halide and an electron donating compound (and silicon compound), contacting the ball milled product with a titanium halide with heating to support the titanium and using a catalyst system comprising the thus resulting supported titanium catalyst component, an organo aluminum compound and electron donating compound (Japanese Patent Public Disclosure No. 151691/1977); a method comprising using, in combination, a supported titanium catalyst component prepared by cogrinding, prior to slurry supporting of titanium, an anhydrous magnesium halide and electron donating compound with a halosilane (Japanese Patent Public Disclosure Nos. 108385/1975 and 98076/1977); a polysiloxane (Japanese Patent Public Disclosure No. 20297/1976); a tin or germanium compound (Japanese Patent Public Disclosure No. 87489/1977); or an alcohol of C.sub.6 or more (Japanese Patent Public Disclosure No. 104593/1977); and an organo aluminum catalyst component.
The type (II) catalyst systems have the advantage that supporting of titanium does not require a long time for the preparation of the supported catalyst component, but on the other hand, has the disadvantage on a commercial scale that because of using a titanium halide in excess, steps of recovering, purifying the same, etc. are required. Furthermore, in the polymerization of .alpha.-olefins using the above-described catalyst system, in particular, in the presence of a molecular weight regulator, a number of problems as to both the polymerization activity and stereoregularity are retained with some exceptions. There has further been proposed a method comprising using a catalyst consisting of a supported titanium catalyst component prepared by supporting a titanium tetrahalide by MgX.sub.2.mROH under a slurry state and treating the resulting titanium-containing solid with a solution of an organic acid ester (Japanese Patent Public Disclosure No. 57789/1976), but this method is also insufficient for eliminating polymer deashing.